This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In what has been called the world?s worst mass poisoning, between 35 and 70 million people are affected by chronic low-level arsenic poisoning in Bangladesh and surrounding areas. We have previously suggested that this poisoning is not directly due to the toxic effects of arsenic, but is instead primarily due to arsenic-induced selenium deficiency. We plan to build on our earlier work to provide a molecular foundation for the treatment of chronic low-level arsenic poisoning in Bangladesh and other affected areas. X-ray absorption spectroscopy (XAS) holds the key to these discoveries.